Radio antenna system



Oct. lfS, 19.45. M. BRUCE RADIb ANTENNA SYSTEM 7 2 Sheets-Sheet 1 FiledApril 8 1944 llllll.

Oct. 16, 1945. M. BRUCE RADIO ANTENNA SYSTEM 2 Sheets-Sheet 2 FiledApril' 8, 1944 Patented Oct. 16, 1945 Male, m ruce, Plymouth,

j ha t a aararswt n miners;

RADIO ANTENNA SYQTEM ass, asslgnor of t ApplicationApril 8, 1944,Serial-No. 530,103

' Clsim m zit-an The present invention relates to antennasystems'andmore particularly to systems wherein the physical dimensionsofthe antenna aresmall relative to the-operating--frequency Theinvention is principally concerned with improvements in antenna systemsfor use on aircraft and other vehicles,'though it possesses a wide fieldof appli-- cation where antenna systems of small dimensionsare required.For anumber of purposes,- a vertical quarterwave elementoperatingagaihst ground possesses certain desirable operatingcharacteristics. Such an a ntenna is non-directional in the horizontalplane, provides radiation with vertical polarization, and isanefiicientradiator. Ihus for general communication purposes it isfrequently desirable toattempt to realizethe characteristics of avertical quarter-wave grounded system. In many instances, however, theopt i tion frequency is such that it is impossi-b1e to employ an antennastructure that even remotely approaches the dimensions of a quarter-waveelement. Particularly is this the easewhere the antennaela ment-is'to-be mounted on vehicles, especially aircraft, where the sizeof theelement is strictly limited to dimensions which are normally resonantonly at'the higher frequencies, For operation at lower frequencies, theequivalent el'ectri cal length of such an element may bebut a smallfraction of a quarter wavelength, possibly 0 Wa elen-gth';forexample;'Reson'ant operation of a short antenna elementis "possible by insertingat the base a load ing circuit having a relatively large valueof'inductive reactance, but suchan arrangement is exceedinglyinefficient. Ihe reason for this is readily apparent when the factorsinfluenc-irig the radiation efficiency of such a system are considered.In general, the radiation eflicie'ncy varies directly as theradiationresistance and inversely as the sum of the radiation and'lossresistances. The radiation resistance of a grounded uarter-wave verticalantenna referr'ed-to the base is approximately 36- ohms. With shorterantennas the radiation resistance is proportionately less, and maybeonly a fractionof anoh'm in the case ofan antenna-that is very shortrela'- tive to its operating frequency." 1

'I'he loss resistanceconsistsof groundlosses and losses in thebaseloading circuit. In so far as vehicle antennas are concerned, theground'losses are generally low because in most instances the eiodn omrrse a: con dm ef m um of hi lyf conductive metallic structure -[Ihe mostim POrtant source" of loss is therefore to "be found in the base loadingcircuit. When the radiation resistance is of the same order as the-1os'ressit ance of the antenna system; the efficiency of the system isunreasonably low, as the power radiated and the power loss 'are of thesameord'er of magnitude. extreme -cas es' the power radiated may be butasmall fraction of the power sup plied to the antenna system. "If,howeventhe radiation resistance of the antenna can beincreasedlappreciably, a substantial improvement may be realized. Where;as in the case under discussion, the loss resistance is ex;- cessive dueto'th'e' insertion at the base'ofi'a' loading circuit having arelatively large value ofinductive reactan'c'e in (ird er tz) attainresonant operation; the p'ossible impr vmentin efficiency which resultsupon even amode'rate ncrease radiation resistance is considerable. It isthere'ore an objectof the invention to provide an intenna system ofsmall-"physical dirn'en'sions'relative to the frequency of operation buthaving relatively highrad iation resistance. 'Anotheriobject of the'invefition is to provide a compact ahdeffic-ient antenna system" whichmay be' readilyadjusted for resonant'operati'on over a relatively widerange of frequencies.

Still another "object of the invention is toprovide an antenna system ofsmallphys'ical' dimensions relativete its operating frequency; aridaving" a' favorable current distribution along g h i M. l "Foricertainpu rposes an antenna system having somewhat differentcharacteristics "than thosetr a quarter-wave antehna may be desired,foreiample those of an un'grounded or'di'pol type of antenna. -Ifheinvention therefore contemplates as still another object the provisionof a Iii'pol'e type antenna which may besmallin size relative to itsoperating frequency but nevertheless caps;

ble of operatingat hig'h efficitency.

Figure 1' illustrates in "schematic fashion one form of the antennasystenfpf the i'nvention, while "Figure Q illustrates in similarfashiona 'di'; pole' antenna system embodying the invention; Figures 3 andillustrate modified: rorms'gr uie antenna system ofthe-invention;IhareaIi'Zation of 'specific embodiments ofthes e systems for particularapplications may be redi'l'y accomplished-bythose skilled-iii the art'{The antenna system of the invention employs r a plurality of closelyspaced substantially parallel linear elements asuch as wires; rods,tubeso'r the -In the case of the grounded type" ahtenna as shown inFigureL- 'these'elements'will' be perpendicular to the surface of theground or structure equivalent to ground. While the spacing betweenelements is preferably a very small fraction of a quarter wavelength,the spacing of these elements is not at all critical and need not beexactly uniform provided that the system is symmetrical. For vehicleuse, the elements may be contained in a simple hollow shell ofinsulating material, the shell having appropriate cgntour fgrthespecific appl c i n- 7 Since e invention '-is' concerned with:antennas are very much shorter, relative t'othe operating frequency,than antennas of convenillustration that the length of each elementv 6may be only /30 of a, wavelength or less of ass'iii tional design, itwill be assumed for purposes of that of a single element antenna. Whenthe anthe desired operating frequency. "Normally an antenna of thislength wouldhave such a low value of radiation resistance that ifbase'10ad-' ing Were attempted in order to attain resonant operation,very little radiation would take place, andsubstantially all thepowersupplied to the antenna wo ld be dissipated by lcssesin the loadingreactance. and ground. 7

As will hereinafter-appear, the radiation eiii cie y,.maybesubstantially increased bythe pro- Yis on o .ap uraht of ante na el e swhich are arranged .in substantially parallel closely spaced relationand operated in phase. In-phase operation vis attained byinterconnectingthe elemen sa a po emot fro the ase tuning means and, adjacent thetop orouter ends, as by the jumperllfl or other low impedance means. In orderthateach elementrnay beadjustecl to resonance,;-separate base-loadingreactancesi2 areprovided betweenjhe, lowenends of the elesupplied by themetallic structure of the vehicle in; case of a: mobile installation.Shielding betweenthe separate reactances is desirable, such indisat d atlax. Y

*In swirl n .ih svs t he radio equipment coupling need be made to one ofthe elements only, since all elements are maintained in phase tennasystem comprises four elements the current ineach' element is one-fourthof the total current and the radiation resistance of each element istherefore approximately four times that through having, their top orfreeends coupledor cqnnected together As -a-result, the excitation oi; one,antenna elementexcites theother elements in, phase; The coupling systemmay comprise an-; inductance 20 coupledto one of the antenna inductancesl2 and connected by a transmission linef iz; of appropriate impedance tothe radio equipment not illustrated.

The improved performance of the above-described, .systemarises from thefact that when several antenna elements are arranged in close proximitygcurrentzin each elementinduces a voltage in-eyery otherelement,givingrise to mutual impedance s suchas exist in any other coupled circuitarrangen ent, The .-resistance component ofthis antenna impedance istheradiation resistanca-while-the reactive component depends upon thetuning of the system and becomes zero at resonance. --The ;multi-tunedin-phase antennagsystemcan,thereforebe consideredas a plu-.

rality of circuits each having a self-impedance; together with a--mutualor transfer impedance relative to every other antenna elementof the of asingle element antenna. "Where the antenna dimensions are such thatnormally the radiation resistance would reach low yalueswith acorresponding reduction in radiation eiiliciency, asin the case of anantenna whose length is a small fraction of a quarter wavelength of thedesired operatin r fequency, the use ofa multi-element system havingindependent base loading means for the individual closely spacedelements permits a substantial increase in radiation efficiency,depending on the number of elementsemployed. Since no increase inheightis required, and as the elements may be very closely spaced, the Jphysical dimensions of the system as a whole are not appreciably largerthan asingle element base loaded system, Since there is no appreciablepotential diflerence be tween corresponding points of the;variousantenna elements, only a minimum -arn ount of insulation need beemployed between the several elements, For aircraft use, the entiresystem might;well be enclosed in a single protective insulatingnclosureof relatively small frontal area A further advantage resultsfrom the fact that for acertain power supplied tothe antenna, thevoltage at the free end will be, practically the same regardless ofwhether; the antenna 4 is; a multi-tuned in-phasesystem or a singleelement system- 'Iheinputvoltage will however be higher in the case ofthe multi -tuned system, due to the increased radiation, resistance atthe base, and accordingly therewill be less variationfinthe voltagestanding wave between the base and-the free endof the antenna.correspondingly, there will be less variation in the currentdistributionbetween these points. The rnqre uniform current distribution on theantenna element substantia l-. ly increases the radiationeficiencybecause the available length of the antenna is more elfe :ti v elyutilized, since the radiation from any' po i nt on, an antenna isproportional to the square' -of the currentat that point, r 4 As theradiation resistance of each antenna element is increased the tuning ;of the system becomes correspondingly more broad, and anged tuningbecomes, practicala By the substantial increase inradiation resistanceachieved 7 through multi-tuned iii-phase operation the use ota base o dnar c of cons e able m itu e is made possible while retaining satisfactory radia; tion efliciencies. As a result,}thegantennaeleri sm b uchhor r t n nvent onal practice dictates, .without 7, sacrifice- ;in;perform ance. I T he-same thqcase ofa dipole orungrounded system-{whichmay be; employed where noground orsin l ct-m3"e principlesandjadvantages fapply anemic equivalent to' ground is available, orwhere the radiation patterniof a dipole" is desired; As .illus tratedin. Figure .2, theasystem is composed of a plurality of: substantiallycolinear elements '30 arranged in pairs to form dipoles. whioharedisposed substantially parallel closely spacedrelation with theirouterends'coupled or .joined by jumper 32 and 34. respectivelyto provideinphase operation. As in the first described arrangement, the length ofeach element may be substantially less than. a quarter-wavelength. ofthe operating frequency, so that the overall length of each-dipole issubstantially less-than the approximately half-wavelength dimensions ofa conventional dipoles To attain resonant operation under theseconditions, inductive reactances 3E arev connected between theinnerendsof each pair ofelements. The reactances are adjustable, and.single control tuning means is preferably provided, as in the previouslydescribed embodiment.. Individual shield 40 are likewise provided, theshields being connected to the mid point of th rea'ctancesenclosedtherein. Coupling to one of the reactances 3B is made by acoupling coil 42 fed by transmission "line 44 from the radio equipment,not shown.

' This system is particularly effective in applicationswhere aJdipoletype antennais ,requiredand where the limitation on physicaldimensions'of the antenna is suchthatthe radiation resistance of aconventional system would bever'y much less than a conventionalhalf-wave antenna of approximately 72 ohms resistance at the center. By:making possible a substantialincrease'in radiation resistance, anefii'cient system may be provided even though the overall dimensionsare-so small that substantial values of loading reactance arenecessaryat the center of each-pairof colinear elements in order toattain resonance at theoperating frequency.

While preferablythe several dipoles-are coupled or connected together ateachend thereof, as illustratedin-Figure 2, it is sufficient if but oneend of each pair of colinear elements or dipole is connected to thecorresponding end of another pair of elements or dipole. Suchinterconnection of one or both ends insures that the dipoles operate inphase, with consequent increase in radiation resistance as compared witha single dipole of similar dimensions. Figure 3 illustrates anarrangement involving bonds 46 at one end only of each dipole.

In certain applications, considerations of space and structure maypreclude the use of either the grounded or the dipole type system. Insuch cases, the modification illustrated in Figure 4 may beadvantageously employed. The system resembles the multiple dipolearrangement of Figure 2 in that the antenna is made up of relativelyshort elements 48 and 50 (in terms of operating frequency) which arearranged in pairs with center-connected loading reactances 52 foradjusting the system to resonance. Each pair of elements constitutes ineffect a bent dipole, with the elements 50 forming an angle with theclosely spaced elements 48. Coupling to the radio equipment (not shown)is by transmission line 54 and coil 56, coupled to one of the loadingreactances. The closely spaced elements 48 have their free endsconnected together by a jumper 58 to insure in-phase operation, withconsequent beneficial increase in the radiation resistance of thesystem.

Having thus described the invention a embodied for purposes ofillustration in systems operating in the manner of groundedquarterwaveand' ungrounded half-wave systems, I'claim asmyinvention: I

1'. A radioantenna system comprising a plurality of closely spacedantenna elements: substantially less than a quarter-wavelength of theoperating frequency in length, a plurality of 'inductively reactivetuning means connected inthean tenna elements in the vicinity of acurrent loop, means. for coupling radio equipment to at least one of"the antenna elements, said elements being spaced less thanaquarter-wavelength apart, and low impedance means connecting saidelements at a. pointremote from the tuning means to providesubstantially in-phase operation of the ele-- ments at the operatingfrequency. 1 "2. A radioantenna system comprising a plurality of closelyspaced antenna elements substantiallyless than a quarter-wavelength ofthe openating frequency in length, individual inductively reactivetuning means connected between each antenna element and ground, andmeans for coupling radio equipment to at least one of said antennaelements, the elements being spaced less than a quarter-wavelength apartand connected by low impedance meansadjacent their free ends to providesubstantially in-phase operation of said elements at the operatingfrequency' '3'. l A radio antenna'system comprising a plurality-ofclosely spaced antenna elements substantially lessthan aquarter-wavelength of the operating frequency in length, individualinductively reactive tunable devices connected betweene'ach antennaelement and ground, 'com-mon actuating means for tuning said devicessimultaneously, means for coupling radio equi'pment'to at least oneof'said antenna elements, said elements being spaced less than-aquarter-wavelength apart, and low impedance means connecting the neeends of said elements to provide substantially iii-phase operation ofsaid elements at the operating frequency, whereby the radiationresistance of the system is caused to be substantially higher than theradiation resistance of a single element system of similar dimensions.

4. A radio antenna comprising a plurality of pairs of closely spacedantenna elements, the elements of each pair being substantiallycolinear, at least one element of each pair having a lengthsubstantially less than a quarter-wavelength of the operating frequency,individual inductively reactive tuning means connected between the innerends of each pair of elements, means for coupling radio equipment to atleast one of said pairs of elements, said pairs of elements being spacedless than a quarter-wavelength apart, and low impedance means connectingsaid elements at a point remote from the tuning means to providesubstantially in-phase operation of the elements at the operatingfrequency.

5. A radio antenna system comprising a plurality of closely spacedantenna elements substantially less than a quarter-wavelength of theoperating frequency in length, individual inductively reactive tuningmeans connected between each antenna element and ground or equivalent,common actuating means for tuning said means, individual shielding meansfor each of said tuning means, means for coupling radio equipment to atleast one of said antenna elements, said elements being spaced less thana quarterwavelength apart, and low impedance means connecting the freeends ofsaid elements to provide substantially in-phase operation of saidelements at the operating frequency, whereby the radiation resistance ofthe system is caused to be Substantially: higher V-than :.a single.element system of similar dimensions. :t p.

6.-A radiolantennav system comprising a pluralityjof pairs,Oficlosely.spaced-antenna elements, the elements; preacher-pair beingsubstantially colinear, each element having alength-jsubstantially lessthan v a, quarter-wavelength of the vpfiratin frequency, individualinductively reactive" tuning means connected, between the inner ends of;each pair, of elements; and means ;for couplingradio equipmentrto atleast one of-said pairs of elements-said pairs ,of elements being spacedless-than a; quarter-wavelength:apartthe outer ends of the. elementsvbeing-c0nnected: to,- gether to provide substantially in-phase: pera:tion of the system attheoperating frequency and Iherebyaffordsubstantially greater radiation resistance than that, of ;a-,singledipole-ofgsimilar n s ns-i-r L 1 .o m7. Aradio antenna system of;thedipole type comprising a plurality ,of-;pairso,f antenna ele-. mentsspaced -.less than, a quarter-wavelength apart, each element havinga-lengthsubstantial ly less than a quarter-wavelength of the oper= atinfrequency, individual inductively reactive tuning means connected-ineach pair of elements in the vicinity of a current loop,common'jactuatingmeansfor tuning said means, individual shielding meansfor each of said tuningmeans, meansfor coupling; radio equipment toatleast one of; said pairs of elements, and means connecting the freeends'of saidelements to pro-'- vide substantially in-phase operation ofthe system at the operating frequency, whereby the radiation resistanceo fvthesystem is caused to be substantially higher than a dipole systememploying a single pair; of elements of similar dimensions.

f 8. A radio antenna system comprising a plue rality of pairs of antennaelements, each element having a length substantially less than aquartervvavelength of-the operating freguencypat-least one element ofeach pair beins disposed in substantially parallel "relation to r at:least 'o'neielementof anotherjpair' and spaced therefrom. :less thana'faquarter-wavelength, individual; inducitivelyreactive vtuning meansconnected-between the elements ."ofv Teach pair, means for :couplingradio: equipment .to at least one of said pairs of elements, a andLmeansl interconnecting said elements i atza point" remote fromthetuning; means tosprovide substantially in-phase operation of thesystem atz the'operating frequency- 7 '7 v l9iiiAradioyantenna systemcomprising a pluralityqlofspairs of antennaelements, eachelem'entzhaving a-length'substantially less than-aquarter-wavelength orthe operating frequency, atleast one element of each pair being disposedinrrsubstantially parallel relation toat leastlone element: .of.anoth'er'pair and, spaced therefrom less; than a quarter-wavelength,individual in dnotively. reactive tuning means connected ;betweenthe-elements of each painmeans for;:cou pling radio equipment to atleast oneo'f said pairs of elements, and means coupling :thefree ends ofthe closely spaced elements to .provid'e substan tially imphaseoperation-of the system .atythe operatingfrequency. V V Q m. 10. A radioantenna system comprising/aplu rality of pairs of antenna elements, eachelement havinga, length substantially less than a quarter. wavelength'ofthe operating frequency, at least one; element of each pair beingdisposed insubstantially parallel relation to at least .one element; ofanother-pair and spacedtherefrom less thana quarter-wavelength,individual inductive- 1y, reactive tuning means connected-between theelements of eaonpain common actuatingmeans for tuning said means,individual shieldin means fQneachoisaid tuning means, means for couplingradioequipment to, at least one of -said pairssof antenna elements, andmeans coupling therfree ends of the closely spacedelements to providesubstantially in-phase operation of the system at h e pe at s'fr queny.w a .5 MAL M R GE

